EL116 Test 3-Control Devices

Why are control devices necessary?

Generally to protect wires from overheating and fire

Control devices are an important part of what?

EWIS- Electrical Wire Interface System

Are components in circuits expected to operate simultaneously?

No

What is a switch?

component that breaks circuit by interrupting or diverting current flow

What are some ways switches are actuated?

Manually, temperature, pressure, or mechanical targets

In a double throw switch, what are the three components?

Common (COM), Normally Closed (NC), Normally Open (NO)

What is a momentary switch?

Spring operated, Normally Open, has a triangle on schematic

Five types of switches

Toggles, microswitches, rotary switches, push button, dual in-line parallel (DIP)

What is an SPST?

Single pole, single throw

What is a SPDT?

Single Pole, Double Throw

What is a DPDT?

Double Pole, Double Throw

Most common switch?

Toggle (some w/ detent to prevent accidental actuation)

What does a position switch do?

Determines position of aircraft component (ex: landing gear position, cargo doors open/shut)

What is a microswitch?

Compact position switch (1/16'“)

What kind of switch is a pushbutton switch?

Momentary contact-used for push-to-talk on radio system

Rocker switch?

Rocks to position rather than tripping like a toggle, but functionally equivalent

Rotary Switches

Multiple selections on one switch component, such as Magento selector switch

What is derating?

reduces power output by oversizing the switch component for the load handled

What is derating used for?

Extends life and reliability of devices

What are switch guards?

Prevent accidental actuation (ex: fire supression switches, fuel cutoff switches)-some even have safety wire

What does an annunciator light do?

indicates a certain condition of a switch (ex: Landing gear position lights)

What is a relay?

Remotely operated switch

What is a purpose of a relay?

Control flow of a higher current with a smaller current

What does a relay look like on a schematic?

What is normal labelling for relays?

Relay is denoted by x’s (X1 is pos, X2 is neg), with A1 (N.O.), A2 , and A3 (N.C.) being switch components

Difference between a solenoid and a relay

Solenoid has moveable iron core that will move inside coil when current is applied

Parts of a relay

What is a “direct short”

full system voltage comes into contact with the ground or return side of circuit

Fuse

Used to protect circuit from over-current; typically a filament that melts above a certain amperage

Circuit Breaker

Like a fuse, breaks circuit when current flow exceeds a value. However, it can be reset

Thermal Protector

Protects a motor-opens a circuit when motor temp gets too high

Current Limiter

Like a fuse, opens circuit when current exceeds a value. However, it will stand over current for a short time

Why are relays or solenoids used to start motors?

Motors initially draw a much current than their rated load

Why is derating used on an incandescent lamp?

Cold filament increases resistance and there is up to a 15x current spike

What does the term “Pole” mean?

number of circuits or paths that can be completed through a switch simultaneously

What does the term “Throw” mean?

number of circuits or paths for current per pole or contactor

Relationship between resistance and current in a parallel circuit

Inverse-the path with lowest resistance will have the most current or amperage

What is the best way to describe a double pole, single throw (DPST) switch?

two separate paths opened or closed by a single toggle

Finding current in a parallel circuit if you have the branches?

Add the branches up to find total current (I)

What is a characteristic of current in a DC series circuit?

Single current path-current is constant across all circuit components

What is a key component of voltage in a parallel circuit?

Voltage across each branch is equal to the total source voltage

Ohm’s Law Equation

E=IR, R=E/I, I=E/R

In a standard electromagnetic control devices, what do X1 and X2 refer to?

Connections for magnetic coil (in the relay)

Which switch has high sensitivity and extremely low plunger travel distance?

Microswitch

Primary characteristic of a Normally Open (NO) switch

remains open until actuated by external force

What is the relationship of current (amps) in PARALLEL circuits?

sum of branches equals total current of parallel circuit

Relationship of voltage in PARALLEL circuits

remains same across branches

Relationship of resistance in PARALLEL circuits

Total resistance is the inverse of the sum of the inverses of the branches’ resistances

Relationship of current (amps) in SERIES circuits

current stays same across components

Relationship of voltage in SERIES circuits

sum of voltage across components equals total source voltage

Relationship of resistance in SERIES circuits

Total resistance is equal to sum of resistances across all components in series